A firefighter protective garment is usually a coat or a pant consisting of three or more functional layers of fire-resistant materials. The various layers are normally but not limited to the following:                the outer shell which provides protection against puncture, cuts, abrasion, and heat;        the moisture barrier—consisting usually of a woven or non-woven substrate to which a fire resistant semi-permeable polymer is coated or laminated—which provides resistance to penetration by liquids and blood-borne pathogens while facilitating the transmission of metabolic heat away from the body of the firefighter.        the thermal barrier—usually consisting of an insulating layer of batting or non-woven fabric quilted or laminated to a woven face cloth—which provides the bulk of the resistance to the transmission of heat from the external environment to the body of the firefighter.        
A person being involved in the activities of a firefighter generates metabolic heat that must be dissipated if the person is to maintain healthy bodily function. The principal means by which the clothed firefighter body dissipates metabolic heat is by perspiring. The greatest rate of metabolic heat transfer through perspiration occurs via the mechanism of evaporative cooling and is higher the closer the evaporating perspiration is to the human body. The second mechanism of metabolic heat transfer is evacuation of sensible heat, that is, liquid perspiration contains heat and as that liquid perspiration moves away from the body—through wicking, dripping, etc.—the heat load it contains is also removed from the body. However, evaporation of a given quantity of perspiration evacuates many times more metabolic heat than does the transport of the same quantity of liquid perspiration.
A common configuration and orientation of these layers in a firefighter garment is as follows:
The outermost layer is the outer shell fabric. Moving inwards, the next functional layer is the moisture barrier, orientated with the substrate towards the outer shell and the semi-permeable polymer membrane towards the inside. The next functional layer is the thermal barrier, orientated with the thicker and softer insulating layer facing the moisture barrier film and the face cloth towards the body of the firefighter.
In most common configurations, the thermal barrier is, for the most part and more particularly when wearing a self-contained breathing apparatus (SCBA), in close contact with either the firefighter's clothing or his/her skin. A significant proportion of the firefighter's perspiration cannot therefore, readily evaporate from his/her skin or clothing, but instead must be absorbed by, or wick through, the thermal barrier to effect cooling via the removal of the sensible heat of the liquid perspiration.
Any firefighter garment, including its thermal barrier, must pass stringent performance requirements of NFPA 1971 if the garment is to be certified compliant with this standard and judged suitable for its intended use. Two critical tests in evaluating the protection and comfort of a firefighter protective garment are the Thermal Protective Performance (TPP) test and the Total Heat Loss (THL) test.
The TPP test assesses the ability of the composite structure of a firefighter garment to delay the transfer of radiant and convective heat from the external environment to body of the firefighter and the NFPA 1971 standard mandates a minimum performance standard of 35 (equal to a heat flux of 2 cal/cm2/sec×a minimum elapsed time of 17.5 seconds until the sensor records the equivalent of a 2nd degree burn).
The THL test simulates the transfer of metabolic heat through the composite structure of the firefighter garment from the body of the firefighter to his external environment via the mechanisms of conduction and evaporation. The NFPA 1971 standard mandates a minimum performance rating of 205 W/m2.
TPP performance is, for the most part, inversely proportional to THL performance and a selection and construction of the composite structure of a firefighter garment that increases one will invariably decrease the other.
As currently written, the NFPA 1971 TPP and THL test procedures specify testing of only the composite structure comprising the three component layers of the garment and do not provide for the inclusion of added elements in the test sample.
U.S. Pat. No. 5,001,783A discloses a firefighter garment wherein a spacer element or elements are positioned between two of the layers of the garment. The object of this invention is to incorporate dead-air space in the garment in order to increase the thermal insulating properties thereof. However, by positioning the spacer(s) between two layers of the garment the face cloth fabric of the thermal barrier in direct contact with the uniform or the skin of the firefighter and hence does not provide for a cooling flow of air between the innermost layer of the firefighter protective garment and its wearer. Because the NFPA 1971 TPP and THL test procedures specify testing of only the three component layers of the garment and do not provide for the inclusion of added elements in the test sample it is not obvious that the invention would be able to meet the TPP requirements of the NFPA 1971 standard. Conversely, if the TPP and THL test procedures were modified to include the invention in the test (i.e. with spacers) it is not certain that the garment incorporating this invention could simultaneously meet the TPP and THL requirements of NFPA 1971.
U.S. Pat. No. 3,710,395A discloses an air distribution garment consisting of a layer of an air-permeable, stretchable, compression-resistant, spacer fabric enclosed between layers of stretchable, air-permeable, fabric, having air inlet openings on said garment communicating with manifolds within the garment and through which air is caused to flow over the back and chest portions through the spacer fabric. The object of this invention is to remove excess heat and moisture from the torso to maintain the body in thermal balance. However, the description of the preferred embodiments reveals that the invention is intended to be worn underneath a regular or special-purpose garment and is not intended as a protective garment itself. If it were, the NFPA 1971 performance requirements mandating a level of impermeability to water and to blood-borne pathogens (and as a consequence to air) would render non-compliant with said standard, any firefighter garment incorporating said invention.
U.S. Pat. No. 5,572,991A discloses a firefighter's garment in which in a preferred embodiment the exhaled air from the firefighter's SCBA (Self-Contained Breathing Apparatus) is delivered to the air space or channels between adjacent layers of the garment. The object of the invention is to cool the garment and lower the heat stress on the firefighter. However, to be effective the firefighter must, a priori, be wearing and using his SCBA, a situation that exists, if at all, for a small percentage of the time that a firefighter is wearing his protective garment. Furthermore, because the channels are between adjacent layers of the protective garment the innermost layer, i.e. the thermal barrier, is in direct contact with the garment or skin of the firefighter.
U.S. Pat. No. 5,924,134A discloses a protective garment including an outer shell, a thermal liner and a moisture barrier, in which the thermal liner includes a flame and heat-resistant, apertured, closed-cell foam laminate. The object of the invention is to have a thermal liner that is essentially non-moisture absorbent and that provides high thermal insulation. However, in this invention the thermal barrier of apertured, closed-cell foam is, first, located between the outer shell and the moisture barrier, and second, is a continuous and complete layer rather than a series of discrete, individual elements or spacers. It is nowhere an object of this invention to improve air flow between protective garment and firefighter.
However, in light of the aforementioned, there is still a need for a firefighter garment which, by virtue of its design and components, would be able to provide better air circulation between the garment and the wearer thereof.